I think this comic strip biography by by Jose-Louis Bocquet, Jean-Luc Fromental, and Stanislas Barthélémy, is brilliant:
The Adventures of HergéYou'll see from the reviews on Amazon that not everyone likes it, but I think the negative reviews are missing the point of what its author-illustrators are doing. It's not attempting to be a comprehensive biography, nor to ape Hergé's drawing style. It's more of a series of key moments or telling moments from a life, and plays really nicely between the reality of Hergé's life and his fictional creation, with playful and apt references to the Tintin books seeping into the reality. Maybe some of these fleeting episodes from his life are easier to fully understand if you've already read a more comprehensive traditional biography, though they're generally self-explanatory.
I haven't actually read the Pierre Assouline biography, nor the Benoit Peeters one. The Harry Thompson one is very well written and readable, even though (unauthorised as it was and written without the cooperation of Hergé's estate) it's occasionally factually inaccurate, particularly on the details of Hergé's private life. But maybe that's OK when the ins and outs of Hergé's romantic life hardly seem entirely relevant to his work, nor any of our business! I'm more interested in the processes of how he produced his stories and artwork, and there maybe aren't enough fully detailed and knowledgeable books about that in English.